Image provided by Thomas Kelley on Unsplash.
TL;DR: London’s battle with air pollution dates back centuries. During the Industrial Revolution, coal burning and urban growth led to worsening air quality. The deadly Great Smog of 1952, which caused thousands of deaths, finally spurred effective legislation through the Clean Air Act of 1956. Though fogs persisted for another decade, this marked a turning point. Today, initiatives like Breathe London and Ultra Low Emission Zones (ULEZ) use real-time air quality data to guide policy and protect health.
London was at the epicenter of the Industrial Revolution. From 1850 to 1900, it was one of the largest—if not the largest—cities in the world. Yet, new technologies and urbanization led to abysmal air quality.
The notoriously polluted “London fogs” made their way into both history and literature. This fog cemented itself in the writings of Charles Dickens and Arthur Conan Doyle. Artists such as Monet painted the ominous yellow-grey haze over the city.
Yet thanks to legislative efforts, London’s air quality has improved dramatically, even if the fight for clean air in the city is far from over.
London fog: Pre-1800s
Polluted London fog existed long before even the Industrial Revolution. For centuries, London was colloquially referred to as the “Smoke,” or the “Big Smoke,” due to the infamous combination of mist and air pollution that haunted the city. Accounts of the terrible air quality date as far back as the 1200s. In 1661, the writer John Evelyn published Fumifugium: or, The Inconveniencie of the Aer and Smoak of London Dissipated, a treatise proposing remedies to improve London’s air. Yet Evelyn’s proposals were largely ignored and air quality worsened over time.
London’s air pollution primarily resulted from the burning of wood and sea-coal in homes. Sea coal, an abundant natural resource, provided a cheap alternative to wood. Yet, this soft coal does not burn efficiently, producing more smoke than heat compared to other types of coal. These emissions combined with the naturally occurring mist, creating a dense cloud of smog.
London fog: During & post-1800s
In the 1800s, the situation became truly dire. Industrialization and coal emissions, in particular, drastically increased air pollution. London fogs were yellow and thick, obscuring vision and often referred to as “pea-soupers.” One fog in 1873 caused 268 deaths from bronchitis.
The fogs were particularly bad during the winter months as people burned more coal to heat their homes. Some days, it was so dense, you could not read by daylight. In the 1880s, there were roughly 60 of these terrible fogs per year. Usually, they lasted a few days; however, one fog in 1879 was so severe it blocked out the sun for four months.
Toward the very end of the 1800s and the beginning of the 1900s, air quality in London began to improve. This was due to the adoption of gas heating, the use of electric motors, and the relocation of industry. Yet the notorious London fog was far from gone. In fact, the term “smog” was coined by a Londoner during this time.
Many attempts were made to pass legislation aimed at improving air quality, but these efforts were repeatedly blocked by those supporting coal industry interests. However, a tragedy in the 1950s shifted public opinion and changed the tide.
The Great London Smog of 1952
1952’s Great Smog of London was short-lived. It lasted roughly five days from December 5th to December 9th of that year. Yet, despite its brief existence, this pea-souper was incredibly severe, resulting in at least 4,000 but possibly as many as 12,000 deaths. The polluted fog penetrated indoors, even into hospital wards, and was especially lethal to the elderly and those with underlying illnesses.
Weather conditions contributed to this disaster. An anticyclone trapped emissions near ground level, unable to escape into the atmosphere. A layer of fog, 100 to 200 meters deep, settled over the city. To make matters worse, the winter was particularly cold, increasing the burning of coal for heating.
The Great Smog was composed of several different pollutants. Each day it persisted, the following air pollutants were emitted into the atmosphere:
- Roughly 1,000 tonnes of smoke particles
- About 2,000 tonnes of carbon dioxide
- Around 14 tonnes of fluorine compounds.
- Roughly 140 tonnes of hydrochloric acid
- About 370 tonnes of sulfur dioxide
Due to contact with water particles in the fog, the tonnes of sulfur dioxide were converted into around 800 tonnes of dangerous sulfuric acid.
This fog was so intense that it effectively brought life in London to a halt. Visibility was so poor that, in some parts of the city, people could not even see their own feet. Transportation was disrupted, with people even abandoning cars along the road. Plays and concerts were canceled because audiences could not see the stages, even indoors. Cows reportedly choked to death in fields, and crime rates rose during the Great Smog.
Legislation and improvement
In prior centuries, several kings had attempted to pass legislation limiting the burning of coal, which all proved ineffective. However, after the Great Smog of 1952, Parliament finally enacted successful change.
The government initially dragged its feet, public pressure led to the formation of the Beaver Committee in July 1953. This committee was responsible for investigating air pollution. The reports made by the Beaver Committee ultimately prompted Parliament to pass the Clean Air Act of 1956. This act established areas of the city that were to be smoke-free and restricted the burning of coal in both domestic fires and factories. Homeowners were also offered grants to switch to cleaner heating sources.
After this act was passed, seasonal polluted London fogs continued to occur. In some areas, enforcement of the law remained inconsistent. One particularly notable fog plagued the city in 1962. However, the number of deaths had dropped to several hundred rather than thousands. Fortunately, the polluted fog of 1962 was the last major one to affect the city. Another Clean Air Act was passed in 1968 to pressure authorities to comply with smoke control programs.
Breathe London
Although London is no longer known for polluted fogs, Dr. Laura Jane Smith of Kings College Hospital estimates that there are almost 9,500 air pollution related deaths in the city each year.
London continues to take incredible steps to reduce air pollution. One such initiative is the Breathe London campaign. Breathe London is a network of hundreds of ambient air quality sensors stationed in all 33 city boroughs which provide real-time air quality data. These sensors are installed in locations ranging from hospitals, schools, and parks to roadsides, helping to pinpoint and monitor sources of pollution.
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Breathe London is a collaborative venture. In 2021, the Greater London Authority partnered with Bloomberg Philanthropies to fund the Breathe London sensor network, which is operated by Imperial College London’s Environmental Research Group. The network operates alongside the city’s gold-standard reference monitors to gather the most extensive and high-quality data.
The data collected from Breathe London sensors allows researchers at King’s College London to analyze air pollution’s magnitude and impact on health. This equips community groups with the information they need to organize and provides policymakers with the insights necessary to implement or enforce legislation.
Just as the Beaver Committee’s report led to the Clean Air Act of 1956, access to air pollution data today helps drive positive change.
Ultra low emission zones
The Breathe London network supported the expansion of ultra low emission zones (ULEZ). In 2019, London became the first city in the world to implement these zones. The ULEZ establishes areas in London where vehicles must meet strict emissions or face daily fines, with additional fines for heavy vehicles such as vans and buses. In 2023, ULEZ was expanded to include all of the city’s boroughs.
Across London, ULEZ has effectively reduced nitrogen dioxide concentrations by 27%, which can be observed both by the reference monitoring network and the highly accurate Breathe London Clarity Node-S sensors. Levels of carbon monoxide and particulate matter have also decreased across the city with 97% of vehicles in London now ULEZ-compliant. For some of the most deprived communities, there has been an estimated 80% reduction in people exposed to illegal levels of pollution as of March 2025. ULEZ is effectively protecting public health and addressing air pollution inequality across the city.
Looking forward
London has come a long way, transforming from a cautionary tale about the perils of air pollution into a clean air leader. Gathering data on air pollution is the first step toward meaningful change. Learn how you can invest in air monitoring equipment, to protect public health and the environment.
